<p>Donald Trump promises to bring factory jobs back to the U.S. from overseas, but many blue-collar workers are hurt more by a lack of skills than by globalization. Unskilled assembly-line work has been replaced by so-called advanced manufacturing jobs that require some computer, information technology, or other technical knowledge. In Detroit, Louisville, Grand Rapids, Mich., and other manufacturing hubs, many employers can’t find workers with those skills.</p>